RFID tag

ABSTRACT

An RFID tag, including: a base; an antenna pattern that is provided on the base to form a communication antenna and has a tapered connection end portion which provides a connection terminal to the antenna; an electric conductor that is attached onto the connection end portion of the antenna pattern and is smaller than the connection end portion; and a circuit chip that is electrically connected to the antenna pattern via the electric conductor and performs radio communication by use of the antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and is a Continuation-In-Part, claimingpriority to U.S. patent application entitled RFID Tag, having Ser. No.11/142,356, by Fujitsu Limited, Kawasaki, Japan, filed on Jun. 2, 2005and incorporated by reference herein. This application also claims thebenefit of Japanese Patent Application No. 2005-081398, filed on Mar.22, 2005, the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an RFID (Radio FrequencyIdentification) tag that performs information exchange with externalequipment in a noncontact manner. Incidentally, among those skilled inthe art related to the technical field of the present application, the“RFID tag” used in the specification of the present application maysometimes be called an “inlay for RFID tag” by regarding the “RFID tag”as an internal component member (inlay) for “RFID tag.” Oralternatively, in some cases, this “RFID tag” may be referred to as “aradio IC tag.” Also, a noncontact type IC card is included in this “RFIDtag.”

2. Description of the Related Art

In recent years, there have been proposed various RFID tags that performinformation exchange with external equipment represented by areader/writer in a noncontact manner by use of radio waves (refer toU.S. Pat. No. 6,239,703B1, for example). As one kind of this RFID tag,there has been proposed an RFID tag in which an antenna pattern forradio communication and an IC chip are mounted on a base sheet made ofplastics or paper. A conceived mode of using an RFID tag of this type issuch that the RFID tag is stuck to an article and the like and performsthe identification of the article by exchanging information on thearticle with external equipment.

In such an RFID tag, a circuit chip and an antenna pattern areelectrically connected together by pinching a micro electric conductorcalled a bump between the circuit chip and an end portion of the antennapattern. The circuit chip is fixed to the above-described base sheet andon this occasion, the area between the circuit chip and the end portionof the antenna pattern except the part occupied by the bump is filledwith an adhesive. As a result, it follows that a micro capacitor isformed, with the circuit chip and the end portion of the antenna patternserving as electrodes. The capacity of such a capacitor that isunnecessary in terms of design is called a parasitic capacity, and aparasitic capacity in an RFID tag has an adverse effect as describedbelow.

There is a type of RFID tag that obtains operating power of an internalcircuit chip from external equipment, and in this type of RFID tag thepower from external equipment is supplied to the circuit chip via anantenna pattern. When at this time, a parasitic capacity exists betweenthe mutually electrically connected circuit chip and end portion of theantenna pattern, the input of operating power from the antenna patternto the circuit chip is interfered with. As a result, there is apossibility that troubles such as the deterioration of the communicationdistance of the RFID tag due to insufficient operating power might becaused.

Therefore, there have been proposed techniques which involve providing,on the antenna pattern side, an adjustment pattern capable of changingan impedance by working such as etching, and adjusting an impedanceincluding the above-described parasitic capacity between the antennapattern and the circuit chip by working this adjustment pattern (referto U.S. Pat. No. 6,535,175B2, for example).

However, such adjustment work has the problem that productivity islowered thereby.

Hence, measures against the above-described parasitic capacity in anRFID tag often involve predicting the parasitic capacity and providing,on the antenna pattern side, a pattern which generates an inductancewhich cancels out the parasitic capacity by a circuital resonance.

The above-described prediction of a parasitic capacity in an RFID tag isperformed on the basis of the area of a portion in which the circuitchip and the end portion of the antenna pattern overlap each other, withthe above-described bump pinched between the two, (an overlappingportion).

However, there are variations in the positional relationship between theabove-described circuit chip and the antenna pattern during themanufacture of an RFID tag, and it is difficult to predict a parasiticcapacity in a stable manner. Furthermore, even when a predictedparasitic capacity is determined beyond the limits of reason and aninductance is found on the basis of the parasitic capacity, in a casewhere an actual parasitic capacity should differ from the predictedparasitic capacity, it becomes impossible to ensure matching between theactual parasitic capacity and the impedance and the above-describedresonance does not occur any more. As a result, the parasitic capacityis not canceled and it follows that the above-described problem ofdeterioration of the communication distance of the RFID tag or the likeoccurs.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesand provides an RFID tag which can be manufactured with highproductivity while avoiding the deterioration of communication distance.

An RFID tag of the present invention is provided with a base, an antennapattern that is provided on the base to form a communication antenna andhas a tapered connection end portion which provides a connectionterminal to the antenna, an electric conductor that is attached onto theconnection end portion of the antenna pattern and is smaller than theconnection end portion, and a circuit chip that is electricallyconnected to the antenna pattern via the electric conductor and performsradio communication by use of the antenna.

In an RFID tag of the present invention, a form in which “the antennapattern has an inductance generation portion that generates aninductance suited to a capacitance between the connection end portionand the circuit chip and prevents performance deterioration of theantenna due to the capacitance” is a typical form.

In an RFID tag of the present invention, the circuit chip overhangs theconnection end part of the antenna pattern, with the electric conductorpinched. As a result, it follows that the circuit chip and theconnection end portion of the antenna pattern overlap each other with agap for the electric conductor. In the part of this portion where thetwo overlap each other (the overlapping portion) except the conductor,there is formed a capacitor which is unnecessary in terms of design,with the circuit chip and the connection end portion which are opposedeach other serving as electrodes. The capacity of this capacitor (theparasitic capacity) is proportional to the area of the overlappingportion and inversely proportional to the gap between the circuit chipand the connection end portion of the antenna pattern in thisoverlapping portion.

Incidentally, in manufacturing an RFID tag of the present invention, itis a general practice to adopt a method by which the electric conductoris attached to the circuit chip and after that, the circuit chip isheated while the circuit chip is being pressed against the base toensure that the electric conductor is attached to the connection endportion of the antenna pattern. When this method is adopted, theelectric conductor, along with part of the connection end portion, sinksinto the base.

In a case where the circuit chip is mounted in such a manner as to beshifted toward the leading end side of the connection end portion, thearea of the overlapping portion becomes narrow and a decreaseproportional to this narrowing of the are occurs in the parasiticcapacity. In this case, the position where the electric conductor isattached to the connection end portion is shifted toward the leading endside of the connection end portion. And because the connection endportion is tapered and its strength decreases toward the leading end,the electric conductor sinks deep into the base, with the result thatthe gap between the circuit chip and the connection end portion of theantenna pattern in the overlapping portion becomes narrow and that anincrease inversely proportional to this narrowing of the gap occurs inthe parasitic capacity. As a result, the above-described decrease andincrease cancel each other out and, therefore, it follows that a changescarcely occurs in the parasitic capacity even when the mountingposition of the circuit chip is shifted toward the leading end side ofthe connection end portion.

On the other hand, in a case where the circuit chip is mounted in such amanner as to be shifted toward the base side of the connection endportion, contrary to the above-described case, the area of theoverlapping portion widens and the gap between the circuit chip and theconnection end portion of the antenna pattern in the overlapping portionwidens. As a result, an increase proportional to the widening of thearea of the overlapping portion and a decrease inversely proportional tothe widening of the gap between the circuit chip and the connection endportion occur in the parasitic capacity and the two cancel each otherout and, therefore, it follows that a change scarcely occurs in theparasitic capacity even when the mounting position of the circuit chipis shifted toward the base side of the connection end portion.

As described above, in an RFID tag of the present invention, theparasitic capacity is stable for manufacturing reasons and, therefore,the parasitic capacity can be predicted in a stable manner. As a resultof this, it is possible to take, as a measure related to a parasiticcapacity, a measure capable of obtaining high productivity withoutimposing burden on manufacturing, for example, providing an antennapattern having an inductance generation portion which causes aninductance determined on the basis of a predicted parasitic capacity tobe generated. In other words, according to the present invention, it ispossible to obtain an RFID tag capable of being manufactured with highproductivity while avoiding the deterioration of communication distance.

As described above, according to the present invention, it is possibleto provide an RFID tag capable of being manufactured with highproductivity while avoiding the deterioration of communication distance.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail based on the following figures, wherein:

FIGS. 1(A) and 1(B) are a front view and a side view, respectively, ofthe first embodiment of the present invention;

FIG. 2 is an enlarged view which shows the shape of a pad of the antennapattern of FIG. 1;

FIGS. 3(A) and 3(B) are an enlarged front view and an enlarged sideview, respectively, of the area near a pad in a case where a circuitchip is mounted in such a manner as to be shifted toward the leading endside of the triangular pad from a standard position;

FIGS. 4(A) and 4(B) are an enlarged front view and an enlarged sideview, respectively, of the area near a pad in a case where a circuitchip is mounted in such a manner as to be shifted toward the base sideof the triangular pad from a standard position;

FIG. 5 is an enlarged view which shows the shape of an antenna patternin an RFID tag of the second embodiment of the present invention;

FIG. 6 is an enlarged view which shows the shape of an antenna patternin an RFID tag of the third embodiment of the present invention; and

FIG. 7 is an enlarged view which shows the shape of an antenna patternin an RFID tag of the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1(A) and 1(B) are a front view and a side view, respectively, ofthe first embodiment of the present invention. However, in the frontview shown here, the internal structure is seen through from the frontof an RFID tag and in the side view shown here, the internal structureis seen through from the side of an RFID tag.

An RFID tag 1 shown in FIGS. 1(A) and 1(B) is constituted by an antennapattern 3 provided on a base sheet 2, a circuit chip 4 which is bondedonto the base sheet 2 with an epoxy adhesive 8 and is electricallyconnected to the antenna pattern via a bump 6, an inductance pattern 5which is electrically connected to the antenna pattern 3 and generatesan inductance, and a cover sheet 7 which covers these antenna pattern 3,circuit chip 4 and inductance pattern 5 and bonded to the base sheet 2.The cover sheet 7 is usually formed from a material selected from amongPET materials, polyester materials, polyolefin materials, polycarbonatematerials, acrylic materials, etc.

In this first embodiment, the above-described base sheet 2, circuit chip4 and bump 6 correspond, respectively, to an example of the base,circuit chip and electric conductor according to the present invention.And a combination of the antenna pattern 3 and the inductance pattern 5corresponds to an example of the antenna pattern according to thepresent invention, and inductance pattern 5 corresponds to an example ofthe inductance generation portion according to the present invention.

This RFID tag 1 receives the energy of an electromagnetic field releasedby a reader/writer as electric energy by use of the antenna pattern 3and the circuit chip 4 is driven by the electric energy, whereby thecommunication action is realized.

This RFID tag 1 is made by performing the following procedure. First,the bump 6 is attached to the circuit chip 4. The end portion of theantenna pattern 3 on the circuit chip 4 side provides a pad 3 a toelectrically connect this antenna pattern 3 to other parts. The circuitchip 4 to which the bump 6 is attached is pressed against the base sheet2 to ensure that the bump 6 is attached to the pad 3 a and at the sametime, the circuit chip 4 is fixed with an adhesive 8 and heated.

The end portion of the antenna pattern 3 on the circuit chip 4 sideprovides the pad 3 a to electrically connect this antenna pattern 3 tothe circuit chip 4 via the bump 6, and this pad 3 a and the circuit chip4 partially overlap each other in such a manner as to pinch the bump 6between the two, with a gap for the bump 6. In the portion where the twooverlap each other (the overlapping portion), the adhesive 8 is filledin the area except the bump 6, with the result that a capacitor which isunnecessary in terms of design is formed in the above-describedoverlapping portion, with the pad 3 a and the circuit chip 4 serving aselectrodes. The capacity of this capacitor (the parasitic capacity)prevents the input of power from the antenna pattern 3 to the circuitchip 4, causing troubles such as the deterioration of the communicationdistance of the RFID tag 1. Therefore, the present embodiment isconstituted in such a manner that by causing a resonance to occurbetween the inductance generated by the inductance pattern 5 provided onthe antenna pattern 3 side and the above-described parasitic capacity,this parasitic capacity is canceled out.

In the present embodiment, the inductance is found using Eq. (1) belowon the basis of a parasitic capacity (standard capacity) which isconsidered to be generated in the overlapping portion of the circuitchip 4 and the pad 3 a on the assumption that the circuit chip 4 ismounted in a standard position determined in performing designing. InEq. (1), “L” is an inductance, “C” is the standard capacity, and “f” isresonance frequency.(2πf)²=1/(L×C)  (1)

On the assumption that the circuit chip 4 is mounted in the standardposition, the standard capacity C is found using Eq. (2) below, wherethe area of the overlapping portion of the circuit chip 4 and of the pad3 a (the standard area) is denoted by “S,” the gap between the circuitchip 4 and the pad 3 a (the standard gap) is denoted by “D,” and thedielectric constant of the adhesive 8 is denoted by “ε.”C=ε×S/D  (2)

Variations ascribed to the accuracy of manufacture etc. exist in themounting position of the circuit chip 4, and hence it follows that thearea of an actual overlapping portion of the circuit chip 4 and of thepad 3 a has some error with respect to the above-described standard areaS. If the area of an actual overlapping portion differs from thestandard area S, also a parasitic capacity which actually occurs in anRFID tag 1 differs from the standard capacity C. Therefore, even whenthe inductance pattern 5 which generates an inductance L is found on thebasis of the standard capacity C, it becomes impossible to ensure thematching given by Eq. (1) between an actual parasitic capacity and theinductance L and hence there is a possibility that the parasiticcapacity may not be canceled out. In the present embodiment, therefore,even when variations occur in the mounting position of the circuit chip4, in order to ensure that an actual parasitic capacity is substantiallyequally to the standard capacity C, that is, the parasitic capacity isstabilized at the standard capacity C for manufacturing reasons, theshape of the pad 3 a of the antenna pattern 3 is contrived as describedbelow.

FIG. 2 is an enlarged view which shows the shape of a pad of the antennapattern of FIG. 1.

In FIG. 2 is shown an enlarged view of the area near the pad 3 a of theantenna pattern 3 in the RFID tag 1 in the present embodiment. As shownin FIG. 2, that the pad 3 a has the shape of a triangle the leading endof which faces the circuit chip 4. Part 3 a-1 of this pad 3 a overlapsthe circuit chip 4. The above-described parasitic capacity is generatedin this overlapping portion. This triangular shape of the pad 3 acorresponds to an example of the “tapered shape” according to thepresent invention.

Even in a case where variations occur in the mounting position of thecircuit chip 4, the triangular pad 3 a shown in FIG. 2 is provided as acontrivance to stabilize the parasitic capacity at the standard capacityC, and the effect obtained from this pad 3 a will be described below.

FIGS. 3(A) and 3(B) are an enlarged front view and an enlarged sideview, respectively, of the area near a pad in a case where a circuitchip is mounted in such a manner as to be shifted toward the leading endside of the triangular pad from a standard position. In this enlargedside view, the internal structure near the pad in an RFID tag 1 is seenthrough from the side. In the present specification, all drawings calledenlarged side views are similar ones.

In the case where a circuit chip 4 is mounted in such a manner as to beshifted toward the leading end side of the triangular pad 3 a from astandard position P, as shown in the enlarged front view of FIG. 3(A),the area of an overlapping portion of the circuit chip 4 and of the pad3 a is narrower than the area of an overlapping portion in a case wherethe circuit chip 4 is disposed in the standard position P, i.e., theabove-described standard area S.

As described above, the circuit chip 4 is pressed against a base sheet2, with a bump 6 pinched between the two. As a result, the bump 6receives a depressing force from the circuit chip 4, and as shown in theenlarged side view of FIG. 3(B), the bump 6, along with part of the pad3 a, sinks into the base sheet 2.

Also, the bump 6 is first attached to the circuit chip 4. For thisreason, when the circuit chip 4 is mounted in such a manner as to beshifted toward the leading end side of the triangular pad 3 a from astandard position P, as in the example of FIGS. 3(A) and 3(B), the bump6 is attached to the part near the leading end on the pad 3 a comparedto the case where the circuit chip 4 is disposed in the standardposition P. Because at this time the pad 3 a is in the shape of atriangle, the width W1 of the pad 3 a in a part where the bump isdisposed, becomes narrower than the width W of the pad 3 a in a partwhere the bump is disposed when the circuit chip 4 is disposed in thestandard position P. As a result of this, the strength of the part ofthe pad 3 a which supports the bump 6 becomes weaker than the strengthobtained when the circuit chip 4 is disposed in the standard position P,and the bump 6 sinks into the base sheet 2 deeper than in the case wherethe circuit chip 4 is disposed in the standard position P. As a result,the gap D1 between the circuit chip 4 and the pad 3 a in the overlappingportion of the circuit chip 4 and of the pad 3 a becomes narrower thanthe gap between the circuit chip 4 and the pad 3 a when the circuit chip4 is disposed in the standard position P, that is, the gap D.

When the circuit chip 4 is mounted in such a manner as to be shiftedtoward the leading end side of the triangular pad 3 a from the standardposition P, as in the example of FIGS. 3(A) and 3(B), as describedabove, the area of the overlapping portion becomes narrower than thestandard area S. As is apparent from Eq. (2) above, the parasiticcapacity of the overlapping portion is proportional to the area of theoverlapping portion and, therefore, the above-described narrowing of theoverlapping portion reduces the parasitic capacity to a level lower thanthe standard capacity C. On the other hand, as is apparent from Eq. (2),the parasitic capacity is inversely proportional to the gap between thecircuit chip 4 and the pad 3 a and, therefore, the shortening of the gapbetween the circuit chip 4 and the pad 3 a increases the parasiticcapacity to a level higher than the standard capacity C. Eventually, adecrease in the parasitic capacity due to the narrowing of the area ofthe overlapping portion is compensated for by an increase in theparasitic capacity due to the shortening of the gap between the circuitchip 4 and the pad 3 a. That is, even when the circuit chip 4 is mountedin such a manner as to be shifted toward the leading end side of thetriangular pad 3 a from the standard position P, as in the example ofFIGS. 3(A) and 3(B), the parasitic capacity in the overlapping portionbecomes almost equal to the standard capacity C.

Next, a description will be given of a case where, contrary to theexample of FIGS. 3(A) and 3(B), a circuit chip 4 is mounted in such amanner as to be shifted toward the base side of a triangular pad 3 a.

FIGS. 4(A) and 4(B) are an enlarged front view and an enlarged sideview, respectively, of the area near a pad in a case where a circuitchip is mounted in such a manner as to be shifted toward the base sideof the triangular pad from a standard position.

In the case of FIGS. 4(A) and 4(B), as shown in the enlarged front viewof FIG. 4(A), the area of the overlapping portion of the circuit chip 4and of the pad 3 a becomes wider than the area of the overlappingportion when the circuit chip 4 is disposed in the standard position P,i.e., the above-described area standard area S. On the other hand, inthis case, the width W2 of the part where the bump 6 is disposed,becomes wider than the width W of the part where the bump 6 is disposedwhen the circuit chip 4 is disposed in the standard position P. As aresult of this, the strength of the part of the pad 3 a which supportsthe bump 6 becomes stronger than the strength obtained when the circuitchip 4 is disposed in the standard position P, and the bump 6 sinks intothe base sheet 2 less deep than in the case where the circuit chip 4 isdisposed in the standard position P. As a result, the gap D2 between thecircuit chip 4 and the pad 3 a in the overlapping portion of the circuitchip 4 and of the pad 3 a becomes wider than the above-describedstandard gap D. The widening of the area of the overlapping portionincreases the parasitic capacity to a level higher than the standardcapacity C, and the widening of the gap between the circuit chip 4 andthe pad 3 a reduces the parasitic capacity to a level lower than thestandard capacity C. Eventually, an increase in the parasitic capacitydue to the widening of the area of the overlapping portion is canceledout by a decrease in the parasitic capacity due to the widening of thegap between the circuit chip 4 and the pad 3 a. That is, even when thecircuit chip 4 is mounted in such a manner as to be shifted toward thebase side of the triangular pad 3 a from the standard position P, as inthe example of FIGS. 4(A) and 4(B), the parasitic capacity becomesalmost equal to the standard capacity C.

As described above by referring to FIGS. 3(A) and 3(B) and FIGS. 4(A)and 4(B), in an RFID tag 1 of the present embodiment, even when themounting position of the circuit chip 4 is shifted from theabove-described standard position P toward the lead end side or the baseside of the triangular pad 3 a, the parasitic capacity becomes almostequal to the standard capacity C. That is, in an RFID tag of the presentembodiment, the parasitic capacity is stable at the standard capacity Cfor manufacturing reasons and, therefore, the inductance L found on thebasis of the standard capacity C works effectively. In this manner, inan RFID tag 1 of the present embodiment, it is possible to find aneffective inductance L in the design stage and hence duringmanufacturing, troublesome work such as the adjustment of inductance isunnecessary and it is necessary only that an inductance pattern asdesigned be made. Therefore, it is possible to manufacture an RFID tag 1of the present embodiment with high productivity while avoiding thedeterioration of communication distance ascribed to the parasiticcapacity.

Incidentally, the “tapered shape” in the present invention is notlimited to the triangular shape in the above-described first embodimentand may be shapes as described below.

In the following, four examples in which the shape of the pad isdifferent from that of the first embodiment will be described as thesecond embodiment, the third embodiment and the fourth embodiment.However, these embodiments differ from the first embodiment only in theshape of the pad, and hence in the following, descriptions will be madeby paying attention to the differences from the first embodiment.

FIG. 5 is an enlarged view which shows the shape of an antenna patternin an RFID tag of the second embodiment of the present invention.Incidentally, in FIG. 5, like reference numerals refer to elementssimilar to the component elements of the above-described firstembodiment.

In an RFID tag 9 shown in FIG. 5, a pad 10 a of an antenna pattern 10 onwhich a bump 6 has a tapered shape with a rounded leading end. In thepresent embodiment, this shape of the pad 10 a produces the same effectas the triangular shape of the pad 3 a of the first embodiment, andvariations in the parasitic capacity ascribed to variations in themounting position of the circuit chip 4 are suppressed, with the resultthat this parasitic capacity becomes stable for manufacturing reasons.

FIG. 6 is an enlarged view which shows the shape of an antenna patternin an RFID tag of the third embodiment of the present invention. Also inFIG. 6, like reference numerals refer to elements similar to thecomponent elements of the above-described first embodiment.

In an RFID tag 11 shown in FIG. 6, a pad 12 a of an antenna pattern 12on which a bump 6 is mounted has a tapered shape the width of whichbecomes narrower by stages toward the circuit chip 4 side. In thepresent embodiment, this shape of the pad 12 a produces the same effectas the triangular shape of the pad 3 a of the first embodiment and thetapered shape of the pad 10 a of the second embodiment with a roundedleading end and variations in the parasitic capacity ascribed tovariations in the mounting position of the circuit chip 4 aresuppressed, with the result that this parasitic capacity becomes stablefor manufacturing reasons.

FIG. 7 is an enlarged view which shows the shape of an antenna patternin an RFID tag of the fourth embodiment of the present invention. Also,in FIG. 7, like reference numerals refer to elements similar to thecomponent elements of the above-described first embodiment.

In an RFID tag 13 shown in FIG. 7, a pad 14 a of an antenna pattern 14on which a bump 6 is mounted has a semicircular shape. In the presentembodiment, this shape of the pad 14 a produces the same effect as thetriangular shape of the pad 3 a of the first embodiment, the taperedshape of the pad 10 a with a rounded leading end of the secondembodiment, and the tapered shape, the width of which becomes narrowerby stages of the pad 12 a, of the third embodiment. Again, variations inthe parasitic capacity ascribed to variations in the mounting positionof the circuit chip 4 are suppressed, with the result that thisparasitic capacity becomes stable for manufacturing reasons.

As described above, according to the RFID tags of the first to fourthembodiments, the parasitic capacity is stable regardless of variationsin the mounting of the circuit chip, and hence an inductance effectivefor canceling out the parasitic capacity is found in the design stage.As a result of this, unnecessary troublesome work such as the adjustmentof inductance during manufacturing can be saved and high-productivitymanufacturing becomes possible. That is, it is possible to manufacturethe RFID tags of the first to fourth embodiments with high productivitywhile avoiding the deterioration of communication distance ascribed tothe parasitic capacity.

In the foregoing, as examples of the antenna pattern according to thepresent invention, the descriptions were given of four examples of theantenna pattern 3 having the triangular pad 3 a, the antenna pattern 10having the tapered pad 10 a with a rounded leading end, the antennapattern 12 having the tapered pad 12 a in which the width decreases bystages toward the circuit chip side, and the antenna pattern 14 havingthe pad 14 a whose shape is semicircular. However, the present inventionis not limited to them. As an antenna pattern of the present invention,any antenna pattern having a pad which becomes narrow toward the leadingend can be used regardless of the shape of the pad.

1. An RFID tag, comprising: a base; an antenna pattern that is providedon the base to form a communication antenna and has a semicircularconnection end portion which provides a connection terminal to theantenna; an electric conductor that is attached onto the connection endportion of the antenna pattern and is smaller than the connection endportion; and a circuit chip that is electrically connected to theantenna pattern via the electric conductor and performs radiocommunication by use of the antenna.
 2. The RFID tag according to claim1, wherein the antenna pattern has an inductance generation portion thatgenerates an inductance suited to a capacitance between the connectionend portion and the circuit chip and prevents performance deteriorationof the antenna due to the capacitance.
 3. The RFID tag according toclaim 1, wherein a parasitic capacity, which occurs in an overlappingportion where the circuit chip and the connection end portion of theantenna pattern overlap each other, is proportional to the area of theoverlapping portion and inversely proportional to a gap between thecircuit chip and the connection end portion of the antenna pattern.